1. Field of the Invention
The present invention relates to a watch with a structure that holds a crown and prevents accidental rotation of the crown.
2. Description of the Prior Art
Some of watches have a structure that locks a crown using screw engagement to prevent accidental rotation of the crown when the watch is worn on the wrist (this structure is hereinafter referred to as “screw lock” or “screw locking structure”).
The screw locking structure is configured such that a winding stem pipe is attached to a case band having a built-in watch movement and a male screw formed on the outer cylindrical surface of a projection disposed outside the case band (hereinafter referred to as “off-case band projection”) of the pipe engages a female screw formed on a crown main portion that fits on the off-case band projection. In a normal operation, this arrangement allows the crown to be locked by engaging the crown main portion with the outer cylindrical surface of the off-case band projection. To perform some operations on the watch movement, the wearer disengages the crown main portion from the male screw, pulls the crown out, and rotates the winding stem accommodated inside the winding stem pipe.
In a conventional watch with such a screw locking structure, watertightness of the portion where the winding stem pipe is attached is generally achieved by brazing the winding stem pipe to the case band (see the JP-A-57-46181, for example).
Another type of watches, which is known in the art, achieves watertightness of the portion where the winding stem pipe is attached by forming a second male screw on the winding stem pipe that is different from the male screw that engages the crown, engaging the second male screw with a female screw formed on a pipe attachment hole in the case band, and sandwiching a watertight gasket between the case band and the winding stem pipe when the screws engage with each other (see the JP-A-2004-245594, for example).
In a watch with a screw locking structure, the female screw of the crown and the male screw of the winding stem pipe that engage with each other may be worn or scraped due to repeated rotation of the crown. This will impair the function of locking the crown, so-called screw locking function.
When such a situation arises, in the watch according to the JP-A-57-46181 in which the winding stem pipe is brazed to the case band, the crown and associated parts cannot be replaced because the replacement involves removal of the winding stem pipe from the case band. Accordingly, the entire watch enclosure assembly including the case band has to be replaced and there is a need to improve this replacement procedure.
In the watch according to the JP-A-2004-245594 in which the winding stem pipe is screwed into the case band, it is believed, in principle, to be able to replace the crown and associated parts including the winding stem pipe. However, every time the crown is engaged with and disengaged from the winding stem pipe, rotational force acts on the winding stem pipe, which may loosen the engagement between the winding stem pipe and the case band and result in reduced watertightness of the watertight gasket.
To overcome the above problem, an adhesive may be filled in the portion where the winding stem pipe and the case band engage with each other. In this case, i.e., when the engagement portion is bonded by an adhesive, it is difficult to remove the winding stem pipe from the case band and practically impossible to replace the crown and associated parts. Accordingly, when the screw locking function is impaired, the entire watch enclosure assembly including the case band has to be replaced and there is a need to improve this replacement procedure.